A light-emitting diode (LED) is a semiconductor device emitting light in response to a current flowing through a compound, such as gallium arsenide. The LED uses a p-n junction structure of a semiconductor into which minority carriers, such as holes or electrons, are injected and emits light through the recombination of the electrons and holes.
The LED has characteristics, such as low power consumption, a relatively long lifespan, ability to be disposed in a narrow space, and strong vibration resistance. In addition, such an LED has been used in a display device and in a backlight unit thereof. Recently, research into applying LEDs to common lighting devices has been conducted. In addition to single color component LEDs, such as red, blue, and green LEDs, white LEDs have been released onto the market. In particular, as white LEDs are applied to products for vehicle lighting devices and general lighting devices, it is expected that demand for the white LEDs will increase sharply.
In LED technology, there are two main methods of realizing white light. The first method is to produce white light by disposing red, green, and blue LEDs to be adjacent to one another and allowing light emitted by the red, green, and blue LEDs to be mixed. However, since the red, green, and blue LEDs have different thermal and temporal characteristics, the ability to mix colors of light uniformly is limited due to changes in tone according to the environment of use and, in particular, the color stains. The second method is to produce white light by disposing a fluorescent material on an LED to allow portions of primary light beams emitted by the LED to be mixed with secondary light beams wavelength-converted by the fluorescent material. For example, a fluorescent material generating yellowish-green or yellow light may be disposed as a light excitation source on a blue LED, whereby white light can be produced by mixing blue light emitted by the blue LED and yellowish-green or yellow excitation light from the fluorescent material. As present, the method of producing white light using a blue LED and a fluorescent material as described above is commonly used.
Recently, quantum dots (QD), able to emit strong light in a narrower wavelength range, as compared to common fluorescent materials, have been used as a material for producing white light. Generally, a QD-LED backlight unit generates white light by irradiating yellow QDs with blue light emitted by a blue LED and uses the generated white light as backlight in a liquid crystal display (LCD) device. A liquid crystal display (LCD) device using such a QD-LED backlight unit has superior color reproducibility, unlike backlight units only using existing LEDs. The liquid crystal display device is able to produce natural color, comparable to natural color generated by an organic light-emitting device (OLED), while manufacturing costs thereof are lower than those of OLED TVs and productivity thereof is high. Accordingly, LCD devices using a QD-LED backlight unit have potential as new displays.
A conventional method of fabricating a QD-LED includes: mixing QDs with a polymer, forming the resultant mixture into a sheet, coating the sheet with a plurality of barrier layers to protect the surface of the sheet from external moisture and increase the lifespan of the sheet. However, since the sheet must be repeatedly coated with the barrier layers, the method has high manufacturing costs. Above all else, the ability to entirely protect QDs from the outside is limited.
Another conventional method includes: etching the surface of glass to a preset depth, introducing QDs to the etched portions of the glass, covering the etched portions with a glass cover sheet, applying low melting point glass to the peripheral portions of the glass cover sheet, sintering the low melting point glass, and forming a seal from the low melting point glass using a laser. However, the process of etching the glass surface increases manufacturing costs. In particular, thin film glass is difficult to use.